A practical, clinical procedure is to be developed for estimating optimum frequency-gain characteristics for both monaural and binaural hearing aids. A wearable master hearing aid, characterized by flexibility of response characteristics, will be used to precisely control frequency-gain characteristics. Part I of the study is concerned with development and evaluation of a clinical procedure for fitting monaural hearing aids. An initial estimate of the optimum frequency-gain characteristic is made on the basis of individual psychoacoustic data. This initial estimate serves as the central cell in a 3 by 3 factorial design in which the low-frequency and high-frequency portions of the frequency-gain characteristic are varied systematically. The object of Part II of the study is to develop an experimental protocol for determining optimum or near optimum frequency-gain characteristics for binaural amplification. The protocol will be an extension of that used in Part I, adding the factor of aided-ear (right vs. left) to the experimental design and using an adaptive procedure to converge on the best estimate of the optimum. Using the information gleaned from Parts I and II of the study, Part III will be concerned with the development and evaluation of a practical, clinical procedure for determining optimum frequency-gain characteristics for binaural amplification.